Here are the programmes and mods you'll need to drive in the "rain" in Assetto Corsa:

Content Manager 0.8.1865.34943 (x86) by Ilja Jusupov:
https://assettocorsa.club/content-manager.html
(Activate "ACC Ext Rain" in Content Manager - Settings - Assetto Corsa - Apps, so you can choose the intensity of raindrops and the velocity of the wipers without installing further programmes.)